1 /*
   2  * Copyright (c) 2012, 2017, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.util;
  26 
  27 import java.util.function.IntConsumer;
  28 import java.util.function.IntSupplier;
  29 import java.util.function.Supplier;
  30 import java.util.stream.IntStream;
  31 
  32 /**
  33  * A container object which may or may not contain an {@code int} value.
  34  * If a value is present, {@code isPresent()} returns {@code true}. If no
  35  * value is present, the object is considered <i>empty</i> and
  36  * {@code isPresent()} returns {@code false}.
  37  *
  38  * <p>Additional methods that depend on the presence or absence of a contained
  39  * value are provided, such as {@link #orElse(int) orElse()}
  40  * (returns a default value if no value is present) and
  41  * {@link #ifPresent(IntConsumer) ifPresent()} (performs an
  42  * action if a value is present).
  43  *
  44  * <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
  45  * class; use of identity-sensitive operations (including reference equality
  46  * ({@code ==}), identity hash code, or synchronization) on instances of
  47  * {@code OptionalInt} may have unpredictable results and should be avoided.
  48  *
  49  * @apiNote
  50  * {@code OptionalInt} is primarily intended for use as a method return type where
  51  * there is a clear need to represent "no result." A variable whose type is
  52  * {@code OptionalInt} should never itself be {@code null}; it should always point
  53  * to an {@code OptionalInt} instance.
  54  *
  55  * @since 1.8
  56  */
  57 public final class OptionalInt {
  58     /**
  59      * Common instance for {@code empty()}.
  60      */
  61     private static final OptionalInt EMPTY = new OptionalInt();
  62 
  63     /**
  64      * If true then the value is present, otherwise indicates no value is present
  65      */
  66     private final boolean isPresent;
  67     private final int value;
  68 
  69     /**
  70      * Construct an empty instance.
  71      *
  72      * @implNote Generally only one empty instance, {@link OptionalInt#EMPTY},
  73      * should exist per VM.
  74      */
  75     private OptionalInt() {
  76         this.isPresent = false;
  77         this.value = 0;
  78     }
  79 
  80     /**
  81      * Returns an empty {@code OptionalInt} instance.  No value is present for
  82      * this {@code OptionalInt}.
  83      *
  84      * @apiNote
  85      * Though it may be tempting to do so, avoid testing if an object is empty
  86      * by comparing with {@code ==} against instances returned by
  87      * {@code OptionalInt.empty()}.  There is no guarantee that it is a singleton.
  88      * Instead, use {@link #isPresent()}.
  89      *
  90      * @return an empty {@code OptionalInt}
  91      */
  92     public static OptionalInt empty() {
  93         return EMPTY;
  94     }
  95 
  96     /**
  97      * Construct an instance with the described value.
  98      *
  99      * @param value the int value to describe
 100      */
 101     private OptionalInt(int value) {
 102         this.isPresent = true;
 103         this.value = value;
 104     }
 105 
 106     /**
 107      * Returns an {@code OptionalInt} describing the given value.
 108      *
 109      * @param value the value to describe
 110      * @return an {@code OptionalInt} with the value present
 111      */
 112     public static OptionalInt of(int value) {
 113         return new OptionalInt(value);
 114     }
 115 
 116     /**
 117      * If a value is present, returns the value, otherwise throws
 118      * {@code NoSuchElementException}.
 119      *
 120      * @apiNote
 121      * The preferred alternative to this method is {@link #orElseThrow()}.
 122      *
 123      * @return the value described by this {@code OptionalInt}
 124      * @throws NoSuchElementException if no value is present
 125      */
 126     public int getAsInt() {
 127         if (!isPresent) {
 128             throw new NoSuchElementException("No value present");
 129         }
 130         return value;
 131     }
 132 
 133     /**
 134      * If a value is present, returns {@code true}, otherwise {@code false}.
 135      *
 136      * @return {@code true} if a value is present, otherwise {@code false}
 137      */
 138     public boolean isPresent() {
 139         return isPresent;
 140     }
 141 
 142     /**
 143      * If a value is not present, returns {@code true}, otherwise
 144      * {@code false}.
 145      *
 146      * @return {@code true} if a value is not present, otherwise {@code false}
 147      */
 148     public boolean isEmpty() {
 149         return !isPresent;
 150     }
 151 
 152     /**
 153      * If a value is present, performs the given action with the value,
 154      * otherwise does nothing.
 155      *
 156      * @param action the action to be performed, if a value is present
 157      * @throws NullPointerException if value is present and the given action is
 158      *         {@code null}
 159      */
 160     public void ifPresent(IntConsumer action) {
 161         if (isPresent) {
 162             action.accept(value);
 163         }
 164     }
 165 
 166     /**
 167      * If a value is present, performs the given action with the value,
 168      * otherwise performs the given empty-based action.
 169      *
 170      * @param action the action to be performed, if a value is present
 171      * @param emptyAction the empty-based action to be performed, if no value is
 172      *        present
 173      * @throws NullPointerException if a value is present and the given action
 174      *         is {@code null}, or no value is present and the given empty-based
 175      *         action is {@code null}.
 176      * @since 9
 177      */
 178     public void ifPresentOrElse(IntConsumer action, Runnable emptyAction) {
 179         if (isPresent) {
 180             action.accept(value);
 181         } else {
 182             emptyAction.run();
 183         }
 184     }
 185 
 186     /**
 187      * If a value is present, returns a sequential {@link IntStream} containing
 188      * only that value, otherwise returns an empty {@code IntStream}.
 189      *
 190      * @apiNote
 191      * This method can be used to transform a {@code Stream} of optional
 192      * integers to an {@code IntStream} of present integers:
 193      * <pre>{@code
 194      *     Stream<OptionalInt> os = ..
 195      *     IntStream s = os.flatMapToInt(OptionalInt::stream)
 196      * }</pre>
 197      *
 198      * @return the optional value as an {@code IntStream}
 199      * @since 9
 200      */
 201     public IntStream stream() {
 202         if (isPresent) {
 203             return IntStream.of(value);
 204         } else {
 205             return IntStream.empty();
 206         }
 207     }
 208 
 209     /**
 210      * If a value is present, returns the value, otherwise returns
 211      * {@code other}.
 212      *
 213      * @param other the value to be returned, if no value is present
 214      * @return the value, if present, otherwise {@code other}
 215      */
 216     public int orElse(int other) {
 217         return isPresent ? value : other;
 218     }
 219 
 220     /**
 221      * If a value is present, returns the value, otherwise returns the result
 222      * produced by the supplying function.
 223      *
 224      * @param supplier the supplying function that produces a value to be returned
 225      * @return the value, if present, otherwise the result produced by the
 226      *         supplying function
 227      * @throws NullPointerException if no value is present and the supplying
 228      *         function is {@code null}
 229      */
 230     public int orElseGet(IntSupplier supplier) {
 231         return isPresent ? value : supplier.getAsInt();
 232     }
 233 
 234     /**
 235      * If a value is present, returns the value, otherwise throws
 236      * {@code NoSuchElementException}.
 237      *
 238      * @return the value described by this {@code OptionalInt}
 239      * @throws NoSuchElementException if no value is present
 240      * @since 10
 241      */
 242     public int orElseThrow() {
 243         if (!isPresent) {
 244             throw new NoSuchElementException("No value present");
 245         }
 246         return value;
 247     }
 248 
 249     /**
 250      * If a value is present, returns the value, otherwise throws an exception
 251      * produced by the exception supplying function.
 252      *
 253      * @apiNote
 254      * A method reference to the exception constructor with an empty argument
 255      * list can be used as the supplier. For example,
 256      * {@code IllegalStateException::new}
 257      *
 258      * @param <X> Type of the exception to be thrown
 259      * @param exceptionSupplier the supplying function that produces an
 260      *        exception to be thrown
 261      * @return the value, if present
 262      * @throws X if no value is present
 263      * @throws NullPointerException if no value is present and the exception
 264      *         supplying function is {@code null}
 265      */
 266     public<X extends Throwable> int orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
 267         if (isPresent) {
 268             return value;
 269         } else {
 270             throw exceptionSupplier.get();
 271         }
 272     }
 273 
 274     /**
 275      * Indicates whether some other object is "equal to" this
 276      * {@code OptionalInt}.  The other object is considered equal if:
 277      * <ul>
 278      * <li>it is also an {@code OptionalInt} and;
 279      * <li>both instances have no value present or;
 280      * <li>the present values are "equal to" each other via {@code ==}.
 281      * </ul>
 282      *
 283      * @param obj an object to be tested for equality
 284      * @return {@code true} if the other object is "equal to" this object
 285      *         otherwise {@code false}
 286      */
 287     @Override
 288     public boolean equals(Object obj) {
 289         if (this == obj) {
 290             return true;
 291         }
 292 
 293         if (!(obj instanceof OptionalInt)) {
 294             return false;
 295         }
 296 
 297         OptionalInt other = (OptionalInt) obj;
 298         return (isPresent && other.isPresent)
 299                 ? value == other.value
 300                 : isPresent == other.isPresent;
 301     }
 302 
 303     /**
 304      * Returns the hash code of the value, if present, otherwise {@code 0}
 305      * (zero) if no value is present.
 306      *
 307      * @return hash code value of the present value or {@code 0} if no value is
 308      *         present
 309      */
 310     @Override
 311     public int hashCode() {
 312         return isPresent ? Integer.hashCode(value) : 0;
 313     }
 314 
 315     /**
 316      * Returns a non-empty string representation of this {@code OptionalInt}
 317      * suitable for debugging.  The exact presentation format is unspecified and
 318      * may vary between implementations and versions.
 319      *
 320      * @implSpec
 321      * If a value is present the result must include its string representation
 322      * in the result.  Empty and present {@code OptionalInt}s must be
 323      * unambiguously differentiable.
 324      *
 325      * @return the string representation of this instance
 326      */
 327     @Override
 328     public String toString() {
 329         return isPresent
 330                 ? String.format("OptionalInt[%s]", value)
 331                 : "OptionalInt.empty";
 332     }
 333 }